Method and excitation chamber for spectroscopic analyses



June 30, 1953 F. TODD 2,643,574

METHOD EXCITATION CHAMBER FOR SPECTROSCOPIC ANALYSES Filed Fb. 14, 1951 Patented June 30, 1953 METEOR AND EXCITATIQN QHAiM iBLER F'UR SPEGTROSCOPIC ANALYSES Floyd Todd, Springfield, Pa. Ap sucation'rbruar 14, 1951, Serial No. 210,972

3 Claims.

invention relates to a method and apparat'us for making rapid spectroscopic; analyses in whi'c'h-the substance to be analyzed is dissolved in asuitable electrolyte and the electrolyte is then-introduced into an ex'ctation chamber having-electrodes for creating a submerged are in the electrolyte.

The present invention is concerned primarily with' qualitative analysis employing a -sp'ectrosce'pe. In general; this procedure involves heatin'ga sample of the substance to'be analyzed to incandescence by suitable means of excitation in such a way that the molecules of the sample are disasso'ciated into th ir constituent atoms,- thus emitting light. This light when viewed through the spectroscop'e, produces a series of bright lines which maybe super-imposed ona reference scale and arranged in accordanoe with the wavelengths ofthe light source. Since each chemical element emits" a well known group of lines having wavelengths thatcan be readily recogni'ze'cLa'compari'son of the lines emitted by the sample withstandard reference lines;- enables the operator todetermine what elements are present in the sample.-

Previous methods of spectroscopic analysis are recogniz'e'd to be positive and'accurate but the absence of a suitable excitation chamber or means: for creating' the characteristic lines of the sample, has rendered these methods impractic'ah time-consuming and expensive for many laboratories. For-example, methodsemploying spectrbgraphs and spe'ctrophotometers are com paratively expensive and require many accessor ies. Chemical analysis in general'requii'es" many tests to determine the presence or absence of the elements and relativelydarg-e samples are needed which are usually totally consumed. Much expensive laboratory equipment requiring substantial time for set-up and: manipulation, is inherent in such procedure.

Thepresent method and apparatus on --the otherhand, is ei'ctrernely simple, accurate, in} expensive, and expeditious. For example, the

sensitivity of themethod'and apparatusisillustrated by referring to the following table which gives the limits of detection of allthe common metallic elements except aluminum and otassiurmi together with several rare elements.

Barium 0.07 Mangnesium 0,005 Bismuth 0.9 Manganese 0.07 Cadmium 0.2 Mercury 0.4 Calcium 0.02 Nickel 1.0 cerium" 1.0 Palladium 0.2 Chromium 0.2 Rhodium 0.3

co alt 1.0 Scandiuin- :1 copper 021 saver 003 Eure ium' Sodium 0.009 Gallium" 0:3- strontium 0.02 0 Gold" 02* Thalliun'i 0.1 Indium 0'05}- I'in 02 Iron 05* Titanium 0.6 Lambs-hum 2,01 vanadium 054 Lead 0:? Yttrium 0:1 l0 Lithium 004* zinc 0.06

The limit of dtection for the metallic element as shown in the'foregoing table'is the minimum. concentration expressed in milligrams; per milliliterof test solution in which the individual-elements have been detectedL in accordance with the present invention When more than one metallicelement is present in the sam'etest solution, the limitsof detection;are somewhat higher.

Specifically,- I have found that when two electrodes suchas iron; copper, silver, platinum, tungsten or carbon are immersed in an aqueous solution of an ionizable material such as an acid, base,rsalt, or-mixtures of the same -and whena comparativelylow voltage (for example, -130 volts) is impressed across the" electrodes, theone having- .the lesser surface area exposed to the electrolyte emits a visible arc.

While it wiu be understood'that the above described 'arcing'lcan be produced in acid, neutral or alkaline aqueous solutibnsjl prerertd use-acid or neutral solutions since niet'al' compdunds afe more generally soluble inthe'ml' Also I'pffer to employ ,platinumelectrodes since no characteristic spectroscopic lines for the platinuin'will be emitted. I p

The preferredapparatus for producing" the above described" submerged are comprises 7 a double walled chamber having a fiir-e'dbottom electrode "and an adjustable upper electrdde which are so locatedin the chamber that the-arc produced is inregistry wane small wihd'w in the side of thechamber." Since considerable heat maybe generated during the arcing," coolant is circulatedin-a jacket around the chamberi'a'nd a convenient three-way. valve permits" quick draining of the electrolyte as wen as" subsequent flushing of the interior of the chamber with c601- ant.

A primary objectL-oftli ini'l'entibntherefore, isto provide anexcitation chafiibehhafih'a pair of electrodes capable of being 'submrigd in a liquid in the chamber.

A further "objecfof the iilv'flii'on is tdpfd- Vide-- an improved excitation chamber '1 d1" :S Dkftros'copic analysis, haviiig' a ja'cle't tliidlifli .chamber [8 which support an electrode holder 22.

which coolant may be circulated, a window in registry with enclosed electrodes and a by-pass for circulating coolant into the electrolyte chamher.

A further object of the invention is to provide an improved method of producing a source of illumination for spectroscopic analysis of metalcontaining samples.

Further objects will be apparent from the specification and drawings in which:

Fig. 1 is a perspective showing my improved spectroscopic illumination source conveniently mounted on a bracket and suitable base;

Fig. 2 is a vertical sectional view of the chamber shown in Fig. 1;

Fig. 3 is an enlarged sectional detail showing the source of illumination; and

Fig. 4 is a transverse section as seen at 4-4 of Fig. 2'.

Referring now more particularly to the drawings, a base H], which houses suitable electrical control and safety devices, is provided'with a switch knob H, a rheostat knob l2, input electrical line l3, and output electrical line I 4. A

central post or bracket I 5 on base It supports my improved excitation chamber assembly It by means of a conventional sliding bracket ll. The chamber I6 is preferably made of heat-resistant glass tubing such as Pyrex, having an inner is surrounded by a coolant jacket 19 (Fig. 2). Inner chamber l8 communicates with the neck 20 of the chamber which carries a rubber stopper 2| that is bored to slidably Electrical lead 23 is clamped to holder 22 by means of nut 24 and knob 25. The lower end of holder 22 is transversely apertured at 25 and 21 to support the upper electrode 28 which is preferably a length of platinum wire threaded through apertures 25 and 21 and depending downwardly therefrom. The lower electrode 30 is introduced into chamber I 8 at 3! and is electrically connected to a strap 32 having a binding post 53 to which lead 34 is connected. The electrolyte to be analyzed may be introduced into chamber l8 through a funnel-shaped spout 35, the bore of which is in communication with chamber 18. Coolant for jacket [9 is introduced thereto through conduits 36 and 3'! which communicate with the bottom of the chamber, and coolant I discharge is through spout 38 which has a trap 39 through which the flow of coolant may be observed.

Chamber !8 terminates at its lower end in a narrowed passage 40 which forms one arm of a three-way stopcock 4|. The second arm 42 for the stopcock communicates with coolant passage 36 and in effect provides a by-p-ass for the coolant so that it may be used as a cleaning or flushing medium for chamber 18. The third arm 43 of the stopcock 4| provides a convenient drain for chamber l8 so that either electrolyte or flushing coolant may be removed therefrom.

Electrodes 28 and 30 are preferably centrally aligned in the bore of chamber I 8' so that the gap between the electrodes is in horizontal registrywith a window 45 consisting of a single thickness of glass.

In operation, the. chamber i5 is supported in bracket I? (as shown. in Fig. 1) and the slit housing 45 of a spectroscope (not shown) is directed towards the window 45. A sample to be qualitatively analyzed is introduced into funnel 35 with stopcock 4! in the closed position (as shown in Fig. 2).

A low voltage current of apsubmerged portion 28a proximately volts is then impressed across electrodes 28 and 30'by closing switch H. This causes an arc to occur in the zone around the of the electrode 28 (as The lines emitted by this are are then compared spectroscopically with characteristic reference lines of known elements so that the composition of the sample may be determined.

The method of the present invention requires that the metal or metals of the initial samples be in aqueous solution. There is a wide variety of methods available for accomplishing this, depending upon the nature of the initial sample, which are well known to those skilled in chemistry. Simple water-soluble compounds such as metal salts, certain bases such as sodium hydroxide, and the like, may be merely dissolved in water, heating being resorted to if necessary. In order to facilitate solution it may be desirable to employ an acid, particularly the mineral acids such as nitric acid, hydrochloric acid, sulfuric acid, and the like, thus converting the initial sample into a water-soluble salt of the metal or metals. In this regard, the use of nitric acid is particularly advantageous inasmuch as the metal nitrates are for the most part water-soluble. The concentration of acid employed will depend upon the nature of the initial sample sought to be dis solved. In many cases, a relatively dilute solution such as a solution comprising between about 5% and about 20% of the acid, may be sufficient. However, in certain metal in the initial sample exists in elemental state, as in alloys, it may be necessary to employ a concentrated acid, resorting to heat if necessary, in order to dissolve the sample. For example, with alloys it may be necessary to dissolve the initial material in boiling aqua regia, which the acid solution can be diluted with water to provide the sample for analysis.

In many cases it the initial material to remove therefrom mateshown in Fig. 3).

oils, pharmaceuticals and the like, may be ignited to burn off the organic matter. The ash residue may then be dissolved by an appropriate treatment as discussed above.

One of the primary advantages of the present invention is that only a relatively small volume,

correspondingly larger amounts of the initial sample may be required.

The concentration of the particular metal or metals required in the solution for detection may vary widely, as will be noted from the foregoing table, and will depend not only upon the particular metal but also upon the presence or abcases where, for example, the

sence of other metals. Although the metal or metals may be present in the solution in sumcient amount to be detectable, it may be present in such Weakly ionizable form or of insufiicient concentration by itself to provide visible discharge. In such case, a small amount of a strong acid such as nitric acid, hydrochloric acid, sulfuric acid and the like, or in some cases a known salt such as sodium chloride, may be added to the solution in order to enhance the discharge. In this case, the characteristic spectral lines of hydrogen of the acid (or of the metal of the known salt) will be seen in addition to the spectral lines of the metal or metals present in the same. In general, the tota1 amount of ionizable material present in the solution in order to provide satisfactory visible discharge is at least about and preferably at least about 8% by weight of the solution. The maximum amount that may be present may vary widely and may be as high as about 60% or higher in some cases. however, the amount of ionizable material in the solution is not over about 25%, preferably not over about 20% of the solution.

After the electrolyte containing the unknown sample has been prepared as described above, approximately 2 ml. of the electrolyte is poured into funnel 35. This amount of electrolyte should partially submerge electrode 28 as shown in Fig. 3. the are so that the characteristic lines of the elements in the sample may be detected with the spectroscope. The entire electrolyte solution can then be drained from chamber [8 by turning stopcock 4| to connect arms 40 and 43. turning of the stopcock is then used to flush chamber 18 one or more times, whereupon the next sample is ready for analysis.

It will thus be understood that I have provided an extremely simple and inexpensive apparatus 7 which enables accurate and rapid spectroscopic Normally 9 Switch II is then closed to produce Reverse iii electrolytic solutions, comprising an electrolyte chamber, a pair of electrodes supported in said chamber, a window in the wall of said chamber in registry with the termini of said electrodes, means for adjusting at least one of said electrodes, means for introducing and draining electrolyte into and out of said chamber, and a coolant jacket substantially surrounding said chamher.

2. An excitation chamber for the analysis of electrolytic solutions, comprising an electrolyte chamber, a pair of electrodes supported in said chamber, a window in the wall of said chamber in registry with the termini of said electrodes, means for adjusting at least one of said elec-- trodes, means for introducing and draining electrolyte into and out of said chamber, a coolant jacket substantially surrounding said chamber, and means including a three-way stopcock for bypassing coolant from the jacket into the chamber.

3. A method of analyzing a material with respect to metallic elements therein, which comprises disposing a static body of electrolytic liquid containing said material in solution in surroundiIlg relation to and in contact with a pair of spaced electrodes, with the liquid contacting one of the electrodes over a small area less than the area of liquid contact with the other electrode, applying to the electrodes a low voltage of magnitude to produce a luminous discharge from said one electrode to the electrolytic liquid, and spectroscopically viewing said discharge to distinguish the metallic elements in said material by the characteristic lines in the luminous discharge.

FLOYD TODD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,253,572 Buchanan Jan. 15, 1918 2,282,643 Cutting May 12, 1942 2,390,816. Suits Dec. 11, 1945 2,532,687 Weichselbaum Dec. 5, 1950 OTHER REFERENCES Twyman et al., Estimation of Metals in Solu tion by means of their Spark Spectra, pages 72 through 92 in Proceedings of the Royal Society, A, volume 133 of 1931.

Gibb, Optical Methods of Chemical Analysis, first edition 1942, McGraw Hill Book Co., New York City, page 112 cited. 

